This invention relates to electrical connector apparatus and methods, and more particularly to apparatus and methods for removably connecting electrical wiring to an electronic circuit card or other substrate having a plurality of connection pads located adjacent a peripheral edge thereof.
A common problem in the telecommunications, computer, and electrical control environments, and in many other environments in which electronic technology is applied, is providing suitable electrical and mechanical interconnections between electronic circuit boards, cards or other substrates, and off-card electrical wiring. Printed circuit cards of various types have become the preferred substrate for mounting and interconnecting electronic components, in order to form electronic circuits, subsystems, or complete systems.
Such printed circuit boards are commonly constructed having one or more substantially planer, laminated layers of dielectric material, such as a glass-fiber filled epoxy resin, upon which is applied one or more layers of a conductive material such as copper. The conductive material is typically photographically etched to produce a pattern of individual conductors suitable for interconnecting electronic components which are mounted upon or through the dielectric layers.
While this circuit card construction is predominant in the present-day electronics industry, a variety of other circuit wiring substrates have been developed, and others are expected to be produced in the future. Accordingly, although we typically refer to "printed" circuit cards or boards, it will be understood that the invention disclosed herein will be equally applicable to any relatively thin, substantially planar substrate for supporting and interconnecting electronic components.
In most cases, it is necessary to connect each printed circuit card to other circuit cards, to power supplies, and to a variety of external devices. For example, in telephone switching systems, circuit cards in the switching equipment must be connected to subscriber telephone instruments, batteries, and transmission facilities. In industrial control systems, circuit cards must be connected to measurement and sensing devices, contactors, motors, operator controls and indicators and the like. In virtually every electronic system, some type of electrical wiring is used to connect the circuit card to the external device, and a mechanical and electrical interface between the wiring and the circuit card is required. In modern systems, a standard logic controller is used with many interchangeable external components, and it is highly desireable that all of these components and their associated wiring be quickly changeable.
In the past, it was common to solder wiring directly to circuit boards. However, this practice made it inconvenient to disconnect the circuit board for testing, maintenance, or repair. In addition, the repeated application of heat and stress involved in desoldering and resoldering wires to the circuit board promotes delamination and other damage to the board card. As an alternative, wiring terminal blocks have been developed for permanent installation on circuit cards. The terminal blocks include screw terminals or other means to which external wiring may be removably connected. However, these terminal blocks typically require each wire to be separately connected and disconnected, increasing the cost and time involved in testing or replacing a defective card. In addition, the mechanical process of securing wiring to the terminal blocks can subject the circuit card to stresses that cause damage.
Accordingly, there have been developed a variety of connector structures to provide mechanical and electrical interfaces by which circuit cards may be removably interconnected with external wiring. In one configuration which has achieved high commercial acceptance, a special "card-edge" connector is provided which has a slit-like aperture for receiving a peripheral edge of the circuit card. A plurality of contact pads, typically constructed of the same conductive material as that used for internal interconnections on the circuit card, are provided in a predefined pattern on the exterior surface of the card adjacent the peripheral edge. A plurality of resilient contacts are provided in a corresponding pattern in the connector for electrically mating with the pads on the circuit card.
For each signal lead on the circuit card to which an external connection is desired, a connection is made to one or more of the edge contact pads. When the circuit card is installed in the connector, each of the signals brought to the edge of the card become available at the corresponding contact of the connector. Circuit cards may be easily removed and replaced, severing or making a large plurality of external connections essentially en masse.
Although the prior-art circuit card edge connectors avoid some of the previously mentioned problems associated with the direct attachment of wiring to a circuit card, they create new problems because means must be provided to attach such wiring to the connector. In one prior art approach, the edge connector is itself soldered to an auxiliary circuit card, and wiring may be directly attached to the auxiliary card. The wiring may be soldered to the auxiliary circuit card, or terminal blocks or other connection means may be provided. This is an inadequate solution, because the direct attachment of wiring to the auxiliary card presents at least the same problems as have been discussed heretofore with respect to the primary circuit card.
In addition, a large number of connections to a circuit card is typically required, and in many applications, these connections must carry significant amounts of current. As a result, it may be required to connect a substantial bundle of heavy-guage wires to the auxiliary card. These wires can apply significant force to the the circuit cards and to the connector. Since the connections between the wires and the auxiliary circuit card are relatively fragile, these stresses make the connections unreliable, and can easily cause permanent damage the auxiliary circuit card and the connector.
In another prior art approach wire connection terminals are provided on the edge connector itself, eliminating the need for an auxiliary circuit card. This arrangement is also unacceptable in many applications. The need to minimize the cost of packaging and housing modern electronic equipment often requires that the equipment be constructed with very little separation between adjacent circuit cards. Accordingly, the density of connectors and wiring required may be very high. In such high-density applications, it becomes progressively more difficult to install wiring on the prior art card edge connectors having terminal blocks because space, and the direction from which the terminals may be accessed, is limited. As each increment of wiring is installed, it tends to block access to the adjacent positions at which the craftsperson is about to install another wire. In addition, as previously noted, the high density of heavy-guage wiring can apply significant stresses to the terminals, the connector, and the circuit card. Prior-art card-edge connectors have failed to properly manage the positions of the wires or the stress they apply to the the terminals and other connector components.
Another problem with prior-art card-edge connectors which are equipped with terminal blocks is that each wire to be attached to the connector must be individually installed and secured by the craftsperson. Because each wire is individually serviced, it is not possible to rapidly connect and disconnect all wiring from the connector for testing or maintenance purposes. Often, the external component to which the wiring may be permanently attached requires maintenance, repair, or replacement. In such instances, it is essential that the component and its wiring be quickly disconnected, and another component immediately connected in its place. The need to install and secure each wire individually makes it impossible to rapidly disconnect one set of wires from the connector and immediately reconnect another set, such as may be desired when retrofitting or changing equipment in applications where only an extremely short period of equipment or circuit unavailability is permissible.
A further disadvantage of these prior-art card-edge connectors is that they generally require a substantial amount of time consuming manual wire preparation after the equipment containing the connectors has been installed. When the equipment is to be connected to external circuits, the external wiring cannot be installed onto the connectors until the equipment itself has been delivered and installed. Thus, once the equipment is delivered, the step of installing the wiring onto the connectors becomes one of the critical paths required to make the equipment operational. When a large number of circuits are involved, the wire installation step requires a substantial amount of time. Due to physical constraints, such as limited space in and near the equipment, it is difficult to shorten this time by applying more craftspersons to the task. Thus, the use of these conventional card-edge connectors lengthens the minimum time required to make equipment operational once it has been installed. Not only is this economically undesirable, it also reduces the ability of manufacturers and equipment operators to respond to emergency or disaster situations by pressing inventoried equipment into service rapidly.